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Published on April 25, 2008; 10.1104/pp.108.120113

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Received April 3, 2008
Accepted April 15, 2008

A pentapeptide motif related to a pigment binding site in the major light-harvesting protein of photosystem II, LHCII, governs substrate-dependent plastid import of NADPH:proto-chlorophyllide oxidoreductase (POR) A

Christiane Reinbothe *, Stephan Pollmann , Phetaphine Phetsarath-Faure , Francoise Quigley , Peter Weisbeek , and Steffen Reinbothe

Universitat Bayreuth, Lehrstuhl fur Pflanzenphysiologie, Universitatsstrasse 30, D-95447 Bayreuth, Germany; Ruhr-Universitat Bochum, Lehrstuhl fur Pflanzenphysiologie, Universitatsstrasse 150, Gebaude ND3/55, D-44801 Bochum, Germany; Universite Joseph Fourier et Centre National de la Recherche Scientifique, FRE3017, CERMO, BP53, F-38041 Grenoble cedex 9, France; Department of Molecular Cell Biology, Utrecht University, Padualaan 8, 3584 Utrecht, The Netherlands

* Corresponding author; email: christiane.reinbothe{at}uni-bayreuth.de.

NADPH:protochlorophyllide (Pchlide) oxidoreductase (POR) A is the only thus far known example of a nucleus-encoded plastid protein that is imported to its final destination in a substrate-dependent, Pchlide-regulated manner. Previous work has shown that the cytosolic PORA precursor (pPORA) does not utilize the general import site but uses a distinct translocon designated the Pchlide-dependent translocon complex (PTC). Here we demonstrate that a pentapeptide motif, Thr-Thr-Ser-Pro-Gly (TTSPG) in pPORA's transit peptide (transA), is involved in Pchlide-dependent transport. Deletion of this motif from the COOH-terminal end of transA abolished both Pchlide binding and protein import. Incorporation of the TTSPG motif into normally non-Pchlide-responsive transit sequences conferred the pigment binding properties onto the engineered chimeric precursors but was insufficient to render protein import substrate-dependent. An additional motif was identified in the NH2-terminal part of transA that was needed for binding of the precursor to the PTC complex. Point mutations of the TTSPG motif identified Gly as the Pchlide binding site. By analogy to the major light-harvesting chlorophyll a/b binding protein of photosystem II, we propose that the peptidyl carbonyl oxygen of Gly may bind directly or via a water molecule to the central Mg atom of the pigment.






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